Sucks, don't it? It's a not helpful error message.
Sadly, rebooting your Mac often is required to get work done in Pr these days. You could also try deleting your prefs, and searching for and quarantining corrupt media.
I believe corrupt media or corrupt projects are the major source of crashes on the Mac side.
And since you're on a Mac, run Disk Warrior and Repair Permissions after all OS upgrades and software installs.
And when you're editing, set your Auto-Save frequency to a short interval, and increase the number of saved projects to 100 or so (I have mine set to 1000.), OR Increment and Save As often. This might save you from losing entire projects to project file corruption, as has happened to me. I have a thread similar to yours now because Pr won't open projects that have been corrupted. I learned about multiple versions the hard way.